As one of methods to enhance an sound insulating property of an automobile interior, there has been conventionally adopted a method of providing a sound insulating structure along a beltline of the automobile. As such a sound insulating structure, for example, Patent Reference 1(JP-A 2001-219738) discloses a sound insulating structure in which, at a door glass closed time, sound insulators are provided in ones of lower end portions of an outer seal portion and an inner seal portion which are mounted on a door panel, and portions corresponding to the lower end portions of the door glass, and projections elastically contacting the sound insulators are provided in the other of the above.
The sound insulating structure described in Patent Reference 1 intends to prevent intrusion of sound from the automobile exterior by closing a gap between the door panel, concretely, the seal portion provided in the door panel and the door glass, at the door glass closed time, and a certain sound insulating effect can be obtained. However, noise of the automobile interior includes, in addition to sound intruding by air propagation from the automobile exterior, sound generated as a result that various members including a door glass vibrate. A sound insulating property of the automobile interior is expected to be improved by suppressing vibration of the door glass in particular, but in the sound insulating structure of Patent Reference 1, a countermeasure against vibration of the door glass is not considered and a high-level sound insulating performance cannot be obtained.